Form of inorganic nitrogen influences mycorrhizal colonisation and photosynthesis of cucumber

• Published in: Scientia horticulturae Vol. 92; no. 3; pp. 229 - 239
• Main Authors: Valentine, A.J, Osborne, B.A, Mitchell, D.T
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 14-02-2002
• Subjects: Ammonium; Arbuscular mycorrhizas; Cucumis sativus; Nitrate; Photosynthesis; Ammonium; Nitrate; Cucumis sativus; Photosynthesis; Arbuscular mycorrhizas
• ISSN: 0304-4238; 1879-1018
• DOI: 10.1016/S0304-4238(01)00302-8

The effects of arbuscular mycorrhizal (AM) colonisation by
Glomus mosseae (Nicolson and Gerdemann) Gerdemann and Trappe on growth and photosynthesis of cucumber (
Cucumis sativus L. cv. Telegraph Improved) were studied using plants supplied with low phosphorus (0.13
mM P) nutrient solutions containing nitrate (NO
3
−), ammonium (NH
4
+) or a NO
3
−/NH
4
+ mixture, with the same total (4
mM) N concentration. Mycorrhizal colonisation varied with N-form; plants supplied with NO
3
− only had the highest total AM colonisation and highest proportion of arbuscules, with no differences between the other two N treatments. Root systems of NH
4
+-fed AM plants had the lowest number of vesicles per unit root length compared with AM plants grown in NO
3
− or NO
3
−/NH
4
+. In the presence of NH
4
+ either on its own or in combination with NO
3
−, both AM and uninoculated plants had higher leaf N concentrations than NO
3
−-fed plants. Tissue P concentrations were less dependent on the form of N supplied, although lower concentrations of P and higher N:P ratios were generally found in the shoot tissues of uninoculated plants in the presence of NH
4
+. Both AM and uninoculated plants had a similar maximum rate of photosynthesis (
P
m), when supplied with NO
3
−. Leaves of AM plants grown in the presence of NH
4
+, had higher
P
m values than uninoculated plants, although this was unrelated to leaf N concentration. They were, however, associated with significantly lower N:P ratios, suggesting that NH
4
+ supply may cause an alteration between N and P metabolism, which can be moderated by AM colonisation. The higher AM-associated values for
P
m were not related to calculated rubisco activities, electron transport capacity or stomatal conductance but may be due, in part, to differences in internal diffusion of CO
2 within the leaf. Despite the lower values for
P
m in uninoculated plants in the presence of NH
4
+ and NO
3
−/NH
4
+ supply, there were no differences in biomass production and the possible reasons for this are discussed.